The Collaborative International Dictionary
Whet slate
Whet \Whet\, n.
The act of whetting.
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That which whets or sharpens; esp., an appetizer. ``Sips, drams, and whets.''
--Spectator.Whet slate (Min.), a variety of slate used for sharpening cutting instruments; novaculite; -- called also whetstone slate, and oilstone.
Wiktionary
whet slate
n. (context mineralogy English) A variety of slate used for sharpening cutting instruments; novaculite; oilstone.